Rotor balancing machine



Dea-23, 1952 K. F. FRANK 2,622,437

'ROTOR BALANCING MACHINE Filed Oct. 30, 1945 6 SheeS--Sheewl l Dec. 23,1952 K. F. FRANK ROTOR BALANCING MACHINE 6 Sheets-Sheet 2 Filed OC'L.50, 1945 PIU-m INVENTOR /Q/QL F.' FRA/VK BY Wm. QM.

Dec. 23, 1952 K. F. FRANK 2,622,437

' RoToR B ALANGING MACHINE Filed OC@ 50, 1945 6 Sheets-Sheet 4 INVENTORTORNEY Dec. 23,

Filedv Oct.

K. F.Y FRANK ROTOR BALANCING MACHINE 6 Sheets-Sheet 5 Y Fe /v/ Mw@ATTORN Y K. F. FRANK ROTOR BALANCING MACHINE Dec. 23, 1952 Filed oct;so, 1945 6 Sheets-Sheet 6 Patented Dec. 23, 195.2

ROTOR BALANGING MACHINE Karl F. Frank, Brooklyn, N. Y., assignor to TheSperry Corporation, a corporation of Delaware Application October 30,1945, Serial No. 625,562

(Cl. '7S-56) 6 Claims.

This invention relates, generally, to the balancing of symmetricalrotating bodies and more particularly, to a novel apparatus especiallyadapted for precision balancing of gyroscope or other high speed rotorsat their normal speed of rotation.

The diliiculties encountered in the use of previous apparatus for thetesting and balancing of moving bodies or machine parts, such asgyroscopic rotors, included the necessity of too many adjustments andoperations when a change from one type of rotor to another was made.Another difficulty encountered with previous balancing machines arose inthe fact that they could not be calibrated to measure the properresultants of static and dynamic unbalances, and they also lacked thenecessary sensitivity for precision balancing.

The determination of the magnitude and position of the unbalance in arotor should preferably be effected while it rotates at a speedapproximating its normal speed of operation.

Further, the position of a Weight unbalance in a rotor must bedetermined with relation to an arbitrary predetermined point on therotor and therefore, in order to locate the position of unbalance, it isnecessary to provide a signal which will continuously give an indicationof the location of that reference point while the rotor rotates. Inapparatus known to the art, means generating a series of potentialimpulses having a frequency corresponding to the speed of rotation ofthe rotor have been provided and these impulses correspond to theinstantaneous position of said predetermined reference point relative toa xed point. These series of potential impulses are produced with theaid of a source of light from which a stationary beam of light isprojected against and reflected by a polished section on thecircumference of the rotating rotor to a photocell.

rlhe point of reflection on the circumference of the rotor thenconstitutes a xed point, While the reference point on the rotor may bearbitrarily selected for example to coincide with one of the borderlines between the polished spot or section and the remaining dullsection of the circumference of the-rotor.

Assuming that the revolving rotor is supported in such manner, forinstance at one end only, that its other end is not restrained frommotion, then, if the rotor is unbalanced, the unbalanced weight willcause the free end of the rotor to perform a swinging or gyratorymovement around the point of support of the rotor, thus causingvibrations of the rotor which have the same frequency as the speed ofrotation of the rotor. It has been proposed to utilize these vibrationsas a means for 'determining the magnitude ofthe unbalance and theposition of the same by causing the vibrations to produce an alternatingpotential having a frequency corresponding to the speed of rotation ofthe unbalanced rotor, and by the aid of such alternating potential todetermine the magnitude of the imbalance, and further, by comparing thephase of said alternating potential with that of the reference signal,i. e., the series of potential impulses, to determine the angularposition of the unbalanced Weight relatively to the predeterminedreference point.

It is noted that all the recent structures employing an electricalpickup arrangement were primarily deficient in one major respect andthat pertained to the fact that none of these structures employed athoroughly free suspension system for holding each end of the testedrotor even though resilient bearing supports were provided because suchdevices as nodal bars and mechanical motivation of the rotor tended toovercome much of the benefits of the resilient supports, and inprecision balancing a certain amount of lost motion resulted by the useof mechanical vibration linkage to the pickup. Furthermore, recentdevelopments did not provide means for accommodating a variety of rotorsbecause the apparatus was encumbered with a nodal bar paralleling therotor and attached to each resiliently suspended bearing support in anunsymmetrical manner. Therefore, whenever a new type or diiierent sizedrotor was to be tested and balanced new nodai points had to be found onthe nodal bar, and substitution of a longer nodal bar was frequentlyrequired. All these adjustments required time and called for more highlyskilled workmen than should be necessary in rapid precision balancingwork.

Also it is noted that some structures known to the art did not providefree suspension means for holding both ends of the rotor while undertest but rather, the rotor was held in an upright position with theupper part free to move with the above characterized motion. Thisarrangement was awkward for mass production use since reversal of therotor, end for end, in the balancing machine was required before acomplete set of dynamic unbalance readings could be obtained. Eventhough some recent developments provided means for eliminating thisreversal of the rotors in balancing tests, the balancing machines stilldemanded a complete adjustment at each of the holding means beforedynamic un..

balance readings could be taken for each end of the rotor. Furthermore,before dynamic unbalance readings could be taken at each rotor end, thebalancing machine would have to be calibrated or set up by placing abalanced rotor with a known unbalanced Weight placed therein at apredetermined reference point. This rotor is then rotated at apredetermined speed after which the proper readings and adjustments weremade in the machine. Since this operation had to be done for both endsof the balanced rotor, it can be readily seen that too many preliminarysteps Were required.

Another diihculty found in the use of some of the known devices forbalancing rotors was the unavoidable inaccuracy of readings taken at thefree end of the rotor, inherently due to the type of suspension used.Careful experiments have shown that if a perfectly balanced rotor isunbalanced as by adding weight at some point along the shaft toward oneend of it, the shaft will, when rotated, with both ends free, perform agyratory movement about a stationary point toward the other end. If theamount of Weight added at the same place along the shaft is increased,the amplitude of gyration is increased. If it is decreased, theamplitude is decreased. But in either case the position of thestationary point remains unchanged. Since accurate unbalance readingscan only be obtained when both ends of the rotor are free to vibrate andthen the readings must be taken at the predetermined stationary pointsafter the planes of unbalance have been selected, it is evident that thedriver of the tested rotor cannot be attached to either end of the rotorin a pivoting arrangement since true or unvariable stationary pointscannot exist due to extraneous causes of rotor vibrations. Attempts havebeen made to filter out these unmeasurable and undesirable vibrations bythe design of the electrical circuit but this has not proved entirelysatisfactory. Also, precision balancing of smooth rotors at their normalhigh speed rotation was impossible in all previous apparatus.

All previous balancing apparatus were not able to correlate theunbalance of the tested rotor due to the continued effect of staticunbalance mode of vibration with dynamic unbalance mode of vibration.That is, all readings taken herev tofore in balancing operations wereanalyzed from a dynamic unbalance mode of vibration viewpoint only.

Therefore, it was an object to devise means which would permit unbalancemeasurements at each end of the rotor representative of true dynamicunbalance with a proper consideration being given to static unbalancewhen it existed.

According to the present invention, a true measure of dynamic and staticunbalances are obtained by using a new system of rotor suspension, rotorholding or adapter means, rotor propelling means and control meanstherefor together with electromagnetic pick-oir units and an electricalmeasuring network.

The problem of rotor suspension was solved by suspending each end of thetested rotor horizontally from three vertically disposed symmetricallyspaced resilient means 120D apart, supporting carrying a cradle holderin which specially designed rotor adapters or cradles for differenttypes of rotors are held by adjustable means. l't is conceivable thatother numbers of resilient means could be used but then the resilienceof each means would have to be reconsidered from a differentmathematical approach. Therefore the invention is not to be limited bysuch a consideration. The problem of obtaining the unbalance readings ata point where the displacement due to pure static unbalance equalled thedisplacement due to pure dynamic unbalance is considered hereinafter. Anadditional problem of rotating smooth rotors without the need ofmechanically or magnetically coupling the rotor was solved through theprovision of a special nozzle for the air drive described in detailhereinafter.

A principal feature of the present invention is the provision of a novelmicro-balancing apparatus to speed up further the mass productionbalancing of symmetrical rotating bodies such as high speed gyroscopicrotors requiring high precision balancing.

A primary object of the present invention is to provide means in a novelbalancing apparatus especially suitable for increased productionbalancing.

Another object of the present invention lies in the provision of noveladjustable mounting and supporting devices with symmetrical radialelements in a novel balancing apparatus that is so constructed andarranged as to substantially eliminate danger of injury to the rotortrunnions While inserting rotors into and removing them from theapparatus. This apparatus utilizes duplicate electrical pickup unitstogether with rotor adapter means insertable into the mounting devices,one pickup unit With associated parts being located a Xed distanceoutwardly of each correction plane correlated with a zero deection pointin the tested rotor. This aparatus further utilizes manually operablemeans for adjusting the separation of the elements radially in themounting devices. Also manually operable means are provided for allowinga horizontal separation of the respective mounting devices when thelongitudinal dimension of the rotor to be tested is different from thepreviously balanced rotor so that unbalance at both ends of the rotormay be determined upon a single insertion of the rotor.

A further object of this invention is to provide a resilient suspensionsystem at each end of the tested rotor in a rotor balancing machine,such suspension being so formed as to provide free vibration at bothends of the rotor when submitted to unbalance forces having both dynamicand static unbalance modes of vibration and further including resilientelements so spaced axially of the rotor that the displacement readingfor a given unbalanced weight is constant regardless of the location ornature of the unbalance.

A further object of this invention is to provide novel air control meansin Which a pressure regulator maintains a steady flow of air against arevolving rotor.

A further object of this invention is to provide a novel air nozzlesuitable for the propulsion of smooth rotors.

A further object of this invention is to provide a novel resilientsuspension for a balancing machine, the resilient elements of thesuspension having a tension such that the suspension is susceptible toboth static and dynamic unbalance modes of vibration.

A further object of the invention is to provide a suspension system inwhich the major supporting elements are perpendicularly disposed.

A further object of the invention is to provide in balancing apparatus asuspension system capable of adjustment to accommodate many types andsizes of rotors.

The invention in another of its aspects relates to novel features of theinstrumentalities described herein for achieving the principal objectsof the invention and to novel principles employed in thoseinstrumentalities, whether or not these features and principles are usedfor the said principal objects or in the said eld.

A further object of the invention is to provide improved apparatus andinstrumentalities embodying novel features and principles, adapted foruse in realizing the above objects and also adapted for use in otherfields.

Other objects and advantages will become apparent from the specificationtaken in connection with the accompanying drawings, wherein oneembodiment of the invention is illustrated.

In the drawings:

Fig. 1 is a perspective View of the novel apparatus of the presentinvention showing an adapter or cradle accommodating a rotor mountedwithin the apparatus for balancing.

Fig. 2 is a front elevational view of the novel balancing apparatus withportions of the left headstock assembly broken away to show details ofthe suspension system correlated with one of the electromagnetic pickupunits, the spindle assembly, the rotor adapter and the unbalancepositional indicator.

Fig. 3 is an elevation view of the left end of the suspension system,taken on line 3 3 of Fig. 2.

Fig. 4 is an elevation of the left end of the suspension system, takenon the line i-li of Fig. 2.

Fig. 5 is a partial plan view of the novel balancing apparatus showingdetails of the airblock assembly and the photoelectric cell and lampassembly.

Fig. 6 is a sectional elevation view of the novel air nozzle used inrotating smooth rotors in the novel balancing apparatus.

Fig. '7 is a schematic wiring diagram of the electrical system partiallyin block form of the novelbalancing apparatus showing its correlationwith the rotor inserted in the suspension system.

Fig. 8 is a wiring diagram of the amplier unit of the novel balancingapparatus showing the details of the block portion in Fig. '7 defined bythe dotted line; and

Fig.,9 is an elevational view, in section, of a novel rotor adapter.

In the drawings, the apparatus is shown as comprising a bedplate l lmounted upon suitable shock-mounts i2, which bedplate carries twoheadstock assemblies i3 slidable lengthwise on machined bedplate waysiii when the clamping screw l5 on the bolt it within a hole of theheadstock is loosened to permit the tongue Il on the lower end of thebolt to be disengaged from an inner wall of the groove I3. By changingthe position of these headstock assemblies, it is possible to check thedynamic unbalance of various types and sizes of rotors. rIhe upper partof headstock assemblies i3 is composed of three arms I9 symmetricallyspaced 120 degrees apart, protruding longitudinally and toward thevertically projected center of the bedplate l l. These arms support acradle holder 2d. Since the headstock assemblies i3 are similar for bothends of the apparatus, only one will be described in detail. Each cradleholder 26 is hung from the three arms i@ in a free suspension systemcomprising resilient means such as helical springs 22. The main body 23of the headstock assemblies I3 is bored horizontally to receive aspindle assembly 24 as shown in Fig. 2. The outside end of the spindleassembly 2li supports an angular locating dial or unbalance positionalindicator 25 cooperating with a xed pointer or index 3|, mounted on astud and screw arrangement 32 while the other end mounts anelectromagnetic pickup unit 26.

Since the pickup units are identical, only one of them, for example, theleft-hand one, will be described in detail, reference being had in thisconnection to Figs. 1 and 2. This pickup instrument 2S comprises one ormore horseshoe magnets 2l provided with a central cylindrical dependingpole 28 of soft iron on which is wound a coil 29. The horseshoe magnet2l is adapted to cooperate with the armature 2l having the form of asoft iron ring that is arranged to be Xed upon the cradle holder 2i! bya forced t. This armature 2l oscillates with the rotor 'axis underinuence of rotor unbalance so that with the central pole 2B insertedthrough the apertured center of armature ring 2l, as shown in the leftportion partially broken away of Fig. 2, the armature 2l is caused tomove in an eccentric path around the pole 28, thereby varying the iluXthrough this pole 2B periodically and generating a voltage in the coil29 having a frequency corresponding to that of the rotor speed.

The spindle assembly 2d is provided with a shaft 33 having a bore ofvarying diameters and varying depths for each diameter to accommodateseveral different sized bolts 35 and a pole shaft 3'! integral with andopposite the depending pole 23. Pole shaft 3l has a shoulder 38 abuttingthe inner surface of horseshoeshaped magnets 2l while the pole shaft isheld within thel bore of the shaft 33 by another bolt or cap screw 34threaded into a hole at the end of the pole shaft 3l. The outside end ofthe shaft 33 is bored a depth suicient to receive the cap screw 3Qrecessed within this shaft a distance permitting a larger threaded borefor the reception of cap screw 35 which retains the angular locatingdial 25 in position over the end of this shaft. A set screw 3d preventsthe dial 25 from turning on the shaft Mounted on the inner end of theshaft 33 is a slip-ring 39 placed over an insulator ring il@ andelectrically connected to the positive output side of theelectromagnetic coil 29 as shown in Fig, 1. This slipring is arranged toturn with the electromagnetic unit 26 when the balancing apparatus isset up for test. A contact brush lil in a brush holder 42 is attached tobut insulated from the headstock body 23 by any convenient means, and aWire G3 is connected to brush lli by a machine screw lid. This wireleads to a pickup potentiometer i5 shown in Fig. 7 and mounted behind apickup potentiometer Calibrating dial i6 shown in Figs. 1 and 2 andmarked leftf A similar dial 4'! marked right exists for the rightelectromagnetic pickup unit. The potentiometers themselves are adjustedby turning knobs de. Returning to the coil 29, it is seen in the circuitof Fig. 7 that the other end of the wire in the coil is grounded at deand a single pole double throw switch 59 is so connected with the rightand left pickup potentiometers 45 that the midpoint of the switch isalways connected to one of the movable contactors of the potentiometer.

The suspension system includes two adjustably spaced groups ofpreferably three adjustable radially disposed, symmetrically arranged 7.resilient elements 120 apart, such as coil springs 22 a common verticalplane with one spring being disposed perpendicularly to carry most ofthe weight of the cradle holder 20 and the rotor mounted in its cradleholder.

The coil springs 22 are connected at their inner ends by 120 spaced pins55 protruding from the surface of the cradle holder 2t on a circularline remote from the rotor cradle or adapter to be described later. Theother end of each of these springs 22 is twisted into a conical form sothat a free end 55 exists substantially in the center of a transversecrosssectional area of each spring, and this free end 56 is Welded at atransverse center of an adjusting screw 5l on its inner end tted into ahole drilled into the free end of each headstock arm i9. All screws 5iare arranged in a common plane at each headstock by careful alignment ofthe holes containing the same. The outside end of each adjusting screwEl carries a knurled nut 58 to give stability to the suspension systemand to the adjusting screws 5l. rhese adjusting screws when freed formovement permit the alignment of each armature 2i with its magnet centerdepending pole 2g.

Each cradle support 2t opposite the armature side is constructed from acylindrical non-magnetic body having a horizontally disposedlongitudinal axis, the body being large enough to permit a wide verticalslot et having a bottom surface defined by a circular arch-shapedsurface 6| whose circumference is tangent to the vertical side walls ofthe slot and whose radius origie nates at the transverse center of thecylindrical body. The radius of the arch and the longitudinal orhorizontal depth of the slot 60 is such that many sizes and types ofrotor adapters can be retained therein. A cradle clamping screw 62protrudes into this slot Gil at a convenient angle to permit firmgripping of a rotor cradle riding on the arch shaped surface or saddle 5I.

An analysis of static and dynamic unbalance of a rotor suspendedaccording to the novel thoroughly free suspension system of thisinvention shows that the distance for the spring separation for aparticular rotor must be calculated in accordance with the expressionwhere wiz in which C=equivalent torsional spring constant in inchpounds/radian, and

where K :lumped spring constant.

Hence, the value of I can bei determined by The suspension systemdescribed heretoforev made it possible to have a denite rotor adapterwith each type of rotor tested and balanced and also brought the pointorY place: of taking unbalance measurements outside of the end' of therotor body itself, i. e., in the' electromagnetic pickup unit 26.` Theproblem of` getting the unbalanceV readings taken at a. point where the'displacement due to pure static imbalance` or an equal amount of puredynamic unbe-lance is the same is solved with an` experimentaladjustable rotor cradle where the lengthV of this cradle' can beselected so that the electromagnetic pick-off units 26 lay in a planenormal to' theaxis of spin of the rotor where the above-mentionedcondition exists.

Resilient elements 22 are dsignedtohavefthe proper tension whendifferent kindsof rotors are balanced so that the two modesof.`vibration mentioned above can be obtained.

The construction ofV the rotor cradle is shown in detail in Fig. 9 andit is mounted in the cradle holders 20 in Figs. 1 and; 2. The cradle oradapter B5 is formed from a rigid body 10 having a substantiallyelliptical torus shapesymmetrical about both axes. The thickness of thehollow Octagon-shaped body 'I'U is suiii'oient for a bore 'H on a minoraxis :c-r. coinciding with a longitudinal axis of the depending pole-28`when the cradle 65 is in the balancing machine, which bore 'Il is largeenough to accommodate a bearing sleeve 'i2 havingan outer endsurface 13of a diameter corresponding to the width of the cradle slot 6B.

Each sleeve 'I2 is locked in place on the rotor adapter 65 by adjustmentscrews 'I4 which t in a vertical hole 16 bored and tapped into the topof each bore 1i. The cradle 65 has ase'ction marked Front on the topside. In preparing the rotors for balancing, the cradle is held withtheportion marked Front" toward the operator and then the rotor is insertedin the cradle or adapter 65 so that it will rotate up and away from theoperator. Next, the left sleeve12 is pushed into the cradle bore on theleft so that its shoulder 15 rests against the rotor cradle and Vthen itis locked in place with the left--hand adjustment screw 14. Now, theright sleeve T2 isp'ressed into the right bore 'H and over the end ofthe rotor shaft. A light nger pressure is applied to the resultantbearing while the right adjustment screw lll is tightened. Some adaptersare additionally marked with an indicia characterization on the top sidefor aligning the sides of the tested rotors for both horizon andVertical gyros. Each rotor is first marked with a darkened surface 11,half-way around its circumference as shown in Fig. 4 and disclosedfurther in the Patent #2,243,- 458 to Esval et al. before it is insertedinto the adapter. The rotor adapter or cradle 65 is locked in the cradleholder 29 by thumb screws 62.

Since the purpose for providing a free suspension system was to avoidsources of vibration which would tend to aiect the accuracy of unbalancereadings taken at each end of the rotor, it becomes necessary to use anon-mechanical drive for the rotor. However, since air drives known tothe art (such as shown in Esval Patent No. 2,243,458) lacked suiiicientcontrol means over the air blast under various conditions of rotoroperation and also since they could not 9, readily be adapted for use inthe testing and the ne precision balancing of the varied 'sizes andtypes of rotors found in mass production manufacture, it becamenecessary to solve these problems by providing new apparatus. Themechanism for controlling the air flow t air nozzle 'IS will bediscussed later. Air block assembly 89 is a fairly heavy rectangularblockshaped body placed centrally longitudinally on the machined waysill of the bedplate ||l but protruding far enough forward toward theoperator over a projection 8| of the bedplate to permit ample room forthe air nozzle 'i8 and another nozzle which may be placed on the top ofthe assembly 8@ nearer the center of smooth rotors. In the bottom rearof the block assembly in Fig. 4 on the right-hand side when viewed fromythe top in the plane view of Fig. 5 there is a vertical duct 83 havinga female threaded entrance to receive the male coupling |34 attached tothe air hose 85 which is brought up from the under side oi bcdplate inthe center thereof Ithrough a hole 85 in the longitudinal center of thebedplate slot i8. In Fig. 5 it is seen that at the top of duct 83another duct 8l is joined thereto at right angles and leads horizontallyforward toward the operator a substantial distance, the terminus ofwhich is joined by still another duct 88 at right angles thereto in ahorizontal plane and projecting inward of the air block assembly 8i).The forward end of du-ct 88 leads to a centrally disposed bore 89 formedin the shape of an upright truncated cone for a substantial distancevertically down in the assembly 8e, while the base of the cone is met bya larger diameter bore 9i?. A rotatable valve e5 in the form of atransversely bored plug or bung is held resiliently against the sides ofthe bore 89 by the spring 95 and plunger 9i seated in a hole S7 boredinto the bottom part of the plug or valve 55. rl`hree ports mi), lill,|02 are bored horizontally into this block substantially at itslongitudinal center and at angles relative to each other to form a Tjunction. Therefore, two ports, EBI-|62, are in line with each other.Valve 95 is lturned about its vertical aXis by a control lever |03fastened to its top by any convenient means such as a machine screw |94.When valve port |99 is .lined up with duct 8B the control lever |63 ispositioned to the lef-t as shown in Fig. 5 and directly under it thelabel Run denotes the Running position of 'the rotor. rIhe ports are soarranged at right angles to each other that a 90 degree counterclockwiserotation of lever |03 will line up ports It-lili with duct 83. Thisposition of the lever |93 is to be associated with the starting of therotor and the label start is inscribed on the top surface of the block89 underneath the lever |33. The start condition of the control valve 95is first considered. In this position port e2 joins a duct e6 at rightangles thereto, parallel with duct 8l, and eX- tends substantially thewhole length of the block 80 so that other spaced ducts lill and |38 maybe joined to duct |05 at right angles thereto. Ducts |61 and |98 lead tovertical ducts |69 and ||l respectively, the top portions of which aredrilled and tapped with a Morse taper to receive either a plug or airnozzle.

In Fig. 4, air nozzle 'F8 is Shown in the exit of port lili! while airplug blocks the exit of port HB. Nozzle "i8 is used when bucket typerotors are tested and balanced.. When smooth rotors are balanced a novelnozzle is necessary and this is inserted where plug is now seated,nozzle 18 having first been removed and replaced by plug The respectivenozzles are held firmly in the Morse taper part of ports |09, |10 bynozzle clamping screws ||2. From this arrangement air may come directlyfrom hose to the nozzle used via channels or ducts 83, 81, 83, portsIBI, m2 shown dotted, ducts |516, |01 and Il. In rthis manner a strongblast may be immediately provided that is sucient to start rotation ofvery heavy rotors.

First, the condition of testing bucket type rotors will be considered.This requires air nozzle '53. Initially, the full blast of air justmentioned is directed against the bucket type rotor from this nozzle andthis onrush of air starts the rotor and produces a fast acceleration ofthe rotor. Soon the control lever E63 is moved to the Run position whichplaces port |06 in line with duct 83. Port lill joined to port it@ leadsthrough a needle valve Il and tubing iid to a pressure regulator i2@situated under the bedplate and then to the nozzle i8 via tubing |29.The needle valve lll is used to adjust the volume of air flowing to thepressure regulator. Needle valve is inserted within the cavity H5 by theusual threaded means. Cavity Il@ has three ducts at right angles to eachother. One duct ||5 leads to port ici. The air once in cavity HB canescape into the nozzle 'i5 by two routes. The route just mentionedrequires a second vertical duct |23 in the bottom of cavity HS. A secondroute starts from a third duct |24 seen in Fig. 5 as being horizontaland at right angles to duct l5 and leads to a pressure regulator by-passvalve |25. Valve |25 contains two ports |26 and l2? at right angles toeach other and when the by-pass valve lever i3@ is rotated to a positionallowing the air to go to duct |05 the pressure regulator is by-passed.This is done when smooth rotors are tested because greater airvelocities are required than for bucket type rotors and if the regulatorld were in the system at this time considerable pressure would be lostthereby. The pressure regulator 20 is adjustable by turning set screw|22 with a screwdriver inserted through the front bedplate hole |2|. Thetesting of smooth rotors requires a special nozzle |3| seen in Fig. 6 toproduce a considerable viscous air drag whereby even fairly heavy smoothrotors are rotated at their normal operating speed. Nozzle I3! is showninserted into a Morse taper hole in the air block leading to duct Hd.The protruding section of nozzle |3| is an elongated body |32 with avertical bore 33, the walls of the bored-body being suiiiciently thickto accommodate drilled and tapped holes into which machine screws |34are screwed to hold a shroud or hood |35. Hood |35 is designed to havean arc section |35 close to and concentric with the rotor G6 below thehorizontal plane |31 a distance such that when the air is directedtangentially to the rotor from the body |32 of the nozzle liti throughan orice |38 drilled at an angle to the top of bore |33 a considerableamount of air is pressed against the surface of the rotor to create aviscous drag. By having the top part of the nozzle body |32 designedwith a rearward slope I3@ suicient clearance is provided between thebody |32 and the lower part of the rotor to make use of a vacuum effectat this point.

The electrical system in the balancing apparatus of this invention issimilar to that disacecha? 11 closed in Patent Number 2,243,457 to Esvalet al. and therefore an elaborate description` of the electrical phaseof this invention is unnecessary. lVIeans for generating a signalproportional to the degree of unbalance ina rotating body has been setforth heretofore and now a description oi the means for locating theangular position of measured unbalance follows.

A photocell and lamp assembly Mil is mounted in the rear of the bedplateII and situated centrally longitudinally thereof by a bracket I4! havinga horizontal slot |42 at the lower end for the reception of a set orclamping screw It?, screwed into the back outside wall of the bedplateII.

Bracket UH has two upper transverse holes for the reception of an armI/l and a housing Idd for the photoelectric cell E52, both revolvablysupported on this bracket. In addition to the adjustment above, arm |65is slide-ble transversely of the bracket in the uppermost of these twoholes. The outside end of arm |45 comprises a sleeve |45 at right anglesto a bearing formed by the portion of this arm entered in the uppermosthole for the slidable support of the lamp housing |44. Housing EM ismovable longitudinally in the sleeve |45' and clamped with a threadedportion of arm E135 and is also pivotally adjustable about the bearingof arm #i5 when knurled thumb screw ISS is loosened. Housing IM containsa conventional lens system IM' at its forward portion.

Any conventional low power consuming lamp Eel shown in Fig. 7 with astandard. socket wired externally to power leads If-l is containedwithin a tubing I5@ snugly fitting within housing lit and movablelongitudinally within the same. Movement of this tubing is prevented bytightening thumb screw Ill?. This arrangement provides an adjustableintensity illumination for projection against the rotor 6B. Reflectiontherefrom is shown as entering the photocell 52 shown in the wiringdiagram of Fig. 7. Photocell |52 is mounted within the housing |45 byany well-known means. By having the bracket MI slidably supported on thebedplate II its position may be changed when the bolt la with a knurledhead is loosened. This makes it possible to align the center of thefront opening in the photocell housing M6 with the light and dark areason the periphery of the rotor. The cell |52 and lamp Vil which areslidably mounted on the bracket Uitl about centers located on an arc thecenter of which lies in the rotor axis so that the cell and lamp may bereadily adjusted to cause their optical axes to intersect at the surfaceof rotors of different diameters.

When a rotor longer than the previously balanced rotor is to bebalanced, both headstock assemblies I3 can be moved along machined waysI4 of the bedplate II after the clamping nuts I5 are loosened. Sinceboth headstocks are movable it is possible by moving each the samedistance to avoid further adjustments of photoelectric cell and lamparrangement |40 when the diameter of the rotor is not materiallydifferent than the previous rotor. By shifting the lamp housing Ill@longitudinally Within the sleeve H25 of mounting arm |45 in the bracketIlI the center of the lamp is positioned horizontally with respect tothe center of the opening in the photoelectric cell housing, androtating the mounting arm and the bracket shifts the angular position ofthe light beam so that the reflected. light enters the. photoelectriccell housing |46'. By rotating. the housing It, it is possible to alignthe opening. in this cell housing with' a reflected light. beam. Fig. 4shows the housing |136 and housing. litt properly oriented relative tothe rotor Ii. The output of photoelectric cell |52. is fed to anelectronic mixer and' attenuator |511 through wires |55. retained at thehousing lit by con-- ventional coupling means |54.

Up to this point several steps in connection with the preparation of themachine for testing and balancing rotors have been described. Thesesteps. included examination of thev suspension systernr the electricalpickup or pick-off' units, the air drive system, the. rotor adapter andthe photoelectric cell and lamp arrangements. Now, it is necessary to.consider how the rotor 66 within its adapter 65 seated within the saddle6I of the cradle holder 2,0 is initially oriented with the pick-oitunits 26 making it unnecessary to calibrate the apparatus with a knownbalanced rotor provided with a given positioned unbalance. This is. doneby aligning the longitudinal center |60 of' the north pole of. eachhorseshoe magnet 21 with. a spot of light |61 projected on the rotor Eilfrom theilamp I 5I within the housing |44 as seen in Fig. 4. Since thereis no'mechanical connection between the electromagnetic pick-oft' units26 containing the' magnets 2l, the above alignment is possible with the.novel spindle mechanism 24 already described. B'y loosening set screw 36on4 the angular locating dial 25 it is seen that thepi'ck-L-oi units.2.6 can. be turnedinto various angular positions without turning dial25. When. the; center line marked |60 in Figs. l and 4 is lined up withthe spot of`light ISI on the rotor as given above, the positionalindicator or locating dial. 25 is turned about the spindle 33 until thezero mark on this dial' 25 is opposite the index nger 3| withoutdisturbing the setting of each north pole. Now the mentioned set screwand machine screw are tightened. Before these settings are made, thesoft iron armature ring 2| press-fitted within the transversely centeredoutside bore of" the cradle holder 20 must be properly centered bothvertically and horizontally with the electromagnet depending pole 23.Such alignment is produced by first unsetting the set screwr 59,loosening each of the knurled nuts 58 in the spring systemv and thenturning the studs 51 until the center of the4 armature 2| coincides withthe center of the depending pole 28. This done, the set screws 59 areset and the nuts 58 tightened. All the above operations and adjustmentsmust be done for both headstock assemblies I3. The weight of the rotor,cradle and cradle holder can be compensated for by an extra turn or twoof the perpendicularly disposed studs 51.

In the circuits known to the art the mixing and attenuating networkwherein electrical phasing is carried out is composed of a transformerand resistance. In applicants corresponding network tl'ie transformerhaving various drawbacks is eliminated and is" substituted by anelectronic arrangement having several electrical control valves. Thisarrangementl eliminates relative phase shift between' the unbalancesignal and the reference signal soi that the phase relation of the twosignals merely depends upon the positioning of the pickup elements onthe machine. Other distinctions will appear as the circuit is described.

Referring to Fig. '7, it can be seen that the previously mentionedpotentiometers 45 mounted vback of the right and left dials 46 and 41respectively in the front panel of the bedplate are connected through asingle-pole double-throw switch 50 to an electronic mixer and attenuator|51 shown in block form. Photoelectric cell |52 generates a referencevoltage (ER) and these voltages are fed to the attenuator and mixer I 51or to the connector |16 shown in Fig. 8. The output of the aboveattenuator and mixer goes to a meter |63 after the voltage signals havebeen filtered by filter |68 and amplified by amplifier |62. Voltages(Ev) proportional to rotor unbalance are created in the coils 29 and arefed to the network |51 through potentiometers 45 and selective switch50. The middle point of the switch 56 is connected to the attenuator andmixer |51. Voltage rectifier |64 and voltage regulator |65 supply poweras shown. With this arrangement unbalanced readings for both the rightand left ends of the rotor can be selectively taken.

Fig. 8 illustrates a composite of the network |51, iilter |6|, amplifier|62, meter |66 and voltage rectier |64 and regulator network |65 in Fig.'1. Since in actual practice the above circuit elements are found withina single container or cabinet having various exterior controls, thetotal circuit arrangement in Fig. 8 is called a balancing machineamplifier unit |1|. Amplifier unit |1| is a linear voltage amplifierwhose indicated output is proportional to the amplitude of the signalinput at a predetermined constant frequency. The input circuit consistsof two separate channels coming into the connector |16 at points markedEv and ER which are associated with the unbalance voltage signals andthe reference voltage signals, respectively. Hence, one channel is forEv and the other is for Ep.. These channels are combined in anelectronic mixing circuit |51 which discriminates the relative phaserelation of Ev with ER. When the selector switch |12 is rotated to afirst position "ER the ER signal is applied to one grid of a twin triodeamplifier tube |13 such as a 6SC7 tube, and the Ev signal is connectedto the ground. In a second position Ev of switch |12, the Ev signal isapplied to the second grid 4of tube |13 and the ER signal is connectedto the ground. Then, in a third position (ER-|Ev) of the same switch,the Ev and ER signals are applied to their respective grids. Thesesignals are mixed by impressing the Ev and ER signals from the two platecircuits of tube 13 Aupon the grid circuit of a triode detectoramplifier tube |14 such as a 6C5 tube. rhe plate output of tube |14 isfed to the wave lter |6l, which determines the frequency response of theamplifier unit |1I. Wave lter |6| is connected to the grid of detectoramplifier tube |15 such as a 605 triode detector which outputs to aresistance biased grid of a duplex-diode triode tube |16 such as the6SQ7 type. The output of this tube is connected to a transformer |11whose secondary is connected back to the diodes of this tube where thesignal is rectified. Meter |63 is connected across the output of tube|16 by conductors, one terminating at a midpoint of the secondary sideof transformer |16 while the other terminates at the cathode of tube|16. Power is supplied to the above tubes from a full wave rectifiertube |88 such as a 5Y3GT type tube, the output of which is regulated bytwo voltage regulator tubes |8| and |82, such as VR|5630 and VRS6-30type tubes, respectively. The A. C. input to the rectier tube |80 isfirst filtered by line voltage lter condensers |63 connected across theprimary of the power transformer |84 to prevent the line voltage frominterfering with the signal voltages Ev and EP.. The output of regulatortube |82 is loaded by two resistors |85 and |66 one of which, such asresistor |86, has a variable contactor |81 which through resistor |88connects to the input transformer connected side of meter |63. It isnoted that resistor |86 is so arranged in this regulator circuit thatcontactor |61 can be maintained at a steady voltage value above groundto buck out any voltage other than the signal voltages from ithepick-01T units to prevent their appearing at the meter |63 during theprocess of zeroing the meter in preparation for the taking of unbalancereadings. This meter zeroing method eliminates extensive iiltering ofripple voltages in the power supply and also eliminates signals pickedup by inductive components of the amplier.

With the selector switch turned to the ER position, a maximum needledeection indicates that'balancing speed has been attained. Thisdeflection can be varied with the ER control |68 which includes a fairlyhigh resistance. Adjustment is had by a movable contactor whosepotential is measured above ground as shown. With the selector switch|12 turned to the Ev position, the meter reading is used to determinethe amount of correction to be applied at a predetermined radius fromthe rotor axis. With the selector switch |12 turned to the ER-l-Evposition, the angular locating dial or indicator 25 will show theunbalance position of the rotor when the meter |63 is zero. Shown nearthe switch |12 is a range switch |9| which functions as a multiplierwhen it is connected to the range adjustment resistors |52-|6i. Whenselector switch |12 is turned on and the range switch I9! is in aposition connecting resistor |62 thereto, a small portion of a large Evsignal is applied to the grid of the first tube |13. Other positions ofthe switch |9| give correspondingly larger portions of the applied Ev asmore resistance is cut out of the signal carrying circuit to this iirsttube |13. The scale to be read on the meter |63 corresponds to theposition of the range switch The actual generation of the Ev and ERsignals is shown and described in this specification as being initiatedby generator action within an electromagnetic pickup imit and byphotoelectrio cell means respectively. The inventive idea of the novelapparatus is not, however, to be limited by such precepts because othertypes of signal generators could be employed.

The meter |63 is made to read zero with no power on the amplifier unit|1| by turning a conventional adjustment screw on the face of the meter.Then, the selector switch |12 is turned to the off position and thepower switch |66 to on If the meter does not indicate Zero after areasonable warm-up period, a meter zero adjustment in the potentiometerresistor |86 may be turned until the meter reads zero. This takes careof alternating current hum causing meter deflection. Vith the light beamfrom the exciter lamp |5| focused on the light area of the rotorSurface, the ER control H96 is adjusted for minimum resistance in thecircuit opposing current flow, and the selector switch |12 is turned tothe ER position. Then, the ER sensitivity control 266, shown in serieswith the potentiometer resistor |96, is adjusted to give a slight needledeliection in the meter |63. The potentiometer resistors 2t@ and I9@having graduated values furnish a condition for minimizing any possibleelectrical phase shift to within ve degrees. This feature eliminates aprevious source o1 inaccuracy in taking positional unbalance readings.

The potentiometers d5 are set so that scales 6 and il associated withsame read about 2. Next, power is turned on the amplier unit VH and theamplier is allowed to warm up. Then the selector switch H2 is turned onto the Ea position. Next, the ER resistance control It@ is adjusted to aposition wherein the minimum amount of resistance in the control opposesthe current iiow. The operator must next rotate the lever it oi thecontrol valve 95 on the air block Se to the Start position shown in Fig.4. The operator should look for the maximum deflection of the meter 253.Then, after the resonant frequency of the wave iilter is reached, theuser can rotate the handle or lever 103 of the control valve 95 to theRun position. If the meter 53 shows an off-scale reading, the operatormust rotate the Ea control i90, until the needle or pointer of thismeter is within the scale. The operator will then rotate the controlvalve handle |03 to the Run position so that he can adjust the needlevalve I i7 by turning the knurled needle valve nut H9 until the meterremains at maximum deflection. The range switch I9! is moved to thefirst position wherein a maximum amount of resistance opposes the Evsignal. Then, the toggle switch E@ on the front of the be-dplate i l isput in the left pickup position.

Selector switch H2 is turned to the Ev position and since the meter iscalibrated in terms of drill depth, the rst drill-depth reading isrecorded for the left end of the rotor. If one is unable to obtain ameter reading in the first position of the range switch E95, otherpositions can be selected to get such reading. f the meter reads 01Tscale in the rst instance, the left potentiometer 45 can be adjusted tokeep meter deiiections within View. Since the amount of unbalance at theleft end of the rotor is now known, the next steps in balancing the sameare to rotate the selector switch H2 to the En position and make the ERmeter reading equal to the Ev meter reading by adjusting the ER controllrnob |96.

Next the selector switch H2 is turned to the En Ev position and the leftangular locating dial is rotated until the needle of the meter E83indicates zero deflection. The reading of dial 25 then gives theposition of unbalance.

The above operations are repeated for the right end of the rotor, andhence, it is necessary to throw the toggle switch 59 to the rightf Theoperation set forth for the left end must normally be repeated in itsentirety for the right end and, in this embodiment, the readingsobtained on the left dial must be applied to the left correction planeof the rotor and the readings obtained from the right dial must beapplied to the right correction plane of the rotor.

Since many changes could be made in the above construction and manyapparently widely diierent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. In a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference voltage of the same frequency as the spin frequency of therotating body and a two-element electromagnetic pick-up device employedat each end of the spin axis of the rotating body to generate a voltagehaving an amplitude proportional to the magnitude of the unbalance massand a phase which when compared with the reference voltage is indicativeof the location of the unbalance mass, the combination of a cradle tosupport the rotating body for rotation about its spin axis, a cradleholder supporting each end of the cradle, each cradle holder beingcoaxial with the spin axis of the rotating body, a headstock assemblyfor each end of the cradle, resilient means interconnecting each cradleholder and its associated headstock assembly, a first element of eachelectromagnetic pick-up device arranged coaxially on its respectivecradle holder, and a second element of each electromagnetic pick-updevice supported in its associated headstock assembly tor independentrotation coaxially of its associated first element.

2. in a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference voltage of the same frequency as the spin frequency of therotating body and a two-element electromagnetic pick-up device isemployed at each end of the spin axis of the rotating body to generate avoltage having an amplitude proportional to the magnitude of theunbalance mass and a phase which when compared with the referencevoltage is indicative of the location of the unbalance mass, thecombination of a cradle having bearing means to support the rotatingbody for rotation about its spin axis, a cradle holder supporting eachend of the cradle, each cradle holder being coaxial with the spin axisof the rotating body, means to secure the cradle in the cradle holders,a headstock assembly for each end of the cradle, a resilient meansinterconnecting each cradle holder and its associated headstockassembly, a first element of each electromagnetic pick-up devicearranged coaxially on its respective cradle holder, and a second elementof each electromagnetic pick-up device supported in its associatedheadstocl; assembly for independent rotation coaxially of its associatedrst element.

3. In a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference Voltage of the same frequency as the spin frequency of therotating body and a two-element electromagnetic pick-up device isemployed at each end of the spin axis of the rotating body to generate avoltage having an amplitude proportional to the magnitude of theunbalance mass and a phase which when compared with the referencevoltage is indicative of the location of the unbalance mass, thecombination of a cradle to support the rotating body for rotation aboutits spin axis, a cradle holder supporting each end of the cradle, eachcradle holder being coaxial with the spin axis of the rotating body, aheadstock assembly for each end of the cradle, each headstock assemblyhaving a plurality of arms extending toward the cradle, a plurality ofresilient means interconnecting each cradle holder to the arms on itsassociated headstock assembly, a rst element of each electromagneticpick-up device arranged coaxially on its respective cradle holder, and asecond element of each electromagnetic pick-up device supported in itsassociated headstock assembly for independent rotation coaxially of itsassociated first element.

4. In a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference voltage of the same frequency as the spin frequency of therotating body and a two-element electromagnetic pick-up device isemployed at each end of the spin axis of the rotating body to generate avoltage having an amplitude proportional to the magnitude of theunbalance mass and a phase which when compared with the referencevoltage is indicative of the location of the imbalance mass, thecombination of a cradle to support the rotating body for rotation aboutits spin axis, a cradle holder supporting each end of the cradle, eachcradle holder being coaxial With the spin axis of the rotating body, aheadstocl: assembly for each end of the cradle, resilient meansinterconnecting each cradle holder and its associated headstockassembly, a first element of each electromagnetic pick-up devicearranged coaxially on its respective cradle holder, a spindle mounted ineach headstock assembly for rotation coaxially of the spin axis of therotating body, and -a second element of each electromagnetic pick-updevice fixed on the spindle of its associated headstock assembly wherebyit is rotatable coaxially of its associated first element.

5. In a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference voltage of the same frequency as the spin frequency of therotating body and a two-element v electromagnetic pick-up device isemployed at each end of the spin axis of the rotating body to generate avoltage having an amplitude proportional to the magnitude of theunbalance mass and a phase which when compared With the referencevoltage is indicative of the location of the unbalance mass, thecombination of a cradle to support the rotating body for rotation aboutits spin axis, a cradle holder supporting each end of the cradle, eachcradle holder being coaxial With the spin axis of the rotating body, aheadstock assembly for each end of the cradle, resilient meansinterconnecting each cradle holder and its associated headstockassembly, a first element of each electromagnetic pick-up devicearranged coaxially on its respective cradle holder, each of the firstelements comprising a soft-iron ring armature, and a second element ofeach electromagnetic pick-up device supported in its associatedheadstock assembly for independent rotation coaxially of its associatedring armature, each of the second elements comprising a U-shaped magnethaving a soft-iron center pole extending into the center of the ringarmature and having a pick-up coil wound on its center pole.

6. In a device to determine the magnitude and location of an unbalancemass in a rotating body wherein means are included to generate areference voltage of the same frequency as the spin frequency of therotating body and a two-element signal pick-up device is employed ateach end of the spin axis of the rotating body to generate a voltagehaving an amplitude proportional to the magnitude of the unbalance massand a phase which when compared with the reference voltage is indicativeof the location of the unbalance mass, the combination of a cradle tosupport the rotating body for rotation about its spin axis, a cradleholder supporting each end of the cradle, each cradle holder beingcoaxial with the spin axis of the rotating body, a headstock assemblyfor each end of the cradle, resilient means interconnecting each cradleholder and its associated headstock assembly, a rst element of eachsignal pick-up device arranged coaxially on its respective cradleholder, and a second element of each signal pick-up device supported inits associated headstock assembly for independent rotation coaxially ofits associated rst element.

KARL F. FRANK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,210,085 Leblanc Dec. 26, 19161,263,325 Klahn Apr. 16, 1918 1,600,569 Sperry Sept. 21, 1926 2,140,398Buckingham Dec. 13, 1938 2,243,457 Esval et al May 27, 1941 2,243,458Esval et al May 27, 1941 2,289,074 Rushing et a1 July 7, 1942 2,293,371Van Degrift Aug. 18, 1942 2,306,625 Hazen Dec. 29, 1942 2,382,673Sihvonen et al. Aug. 14, 1945 2,382,843 Annis Aug. 14, 1945 2,383,588Bousky Aug. 28, 1945 2,405,474 Van De Grift Aug. 6, 1946 2,405,430 KentAug. 6, 1946 2,487,035 Weaver et al Nov. 1, 1949

